TRAWLING REVOLUTIONIZED FISHING. For millennia, humans had been catching fish by net, trap, spear, and hook. The first bottom trawls were 20-foot nets weighted by stones and lead in the closed "cod" end. The front end of the net was held open by a wooden or steel beam. Pulled by a sailboat going with the wind and tide, the trawl raked the seafloor and scared flatfishes like flounder, halibut, and sole into the net.

The first mention of a bottom trawl in historic literature, dug up by Callum Roberts for his definitive history of fishing impacts on the oceans, The Unnatural History of the Sea, was prescient: It was a complaint. In 1376, English fishers wrote to King Edward III to request his intervention in the use of the "wondyrechaun," a weighted net dragged along the seafloor to snatch up anything in its path.

And that the great and long iron of the wondryechaun runs so heavily and hardly over the ground when fishing that it destroys the flowers of the land below water there, and also the spat of oysters, mussels and other fish upon which the great fish are accustomed to be fed and nourished. By which instrument in many places, the fishermen take such quantity of small fish that they do not know what to do with them; and that they feed and fat their pigs with them, to the great damage of the commons of the realm and the destruction of the fisheries, and they pray for a remedy.

The bottom trawl was so unpopular among hook-and-line fishers in Europe that they succeeded in staving off the new and damaging technology for centuries. Its use was banned in several countries and even made a capital offense in France in the 16th century. But as Roberts theorizes in his book, there may have been another reason why the trawl didn't catch on: It caught such volumes of fish--sometimes making the net so heavy it could not be hauled up onto the boat--that the fishers couldn't sell the catch before it spoiled. It wasn't until the advent of railroads and the widespread exportation of ice from Northern Europe that the enormous bounties realized by trawling could actually be utilized. By the 1860s, just 30 years after the world's first steam passenger service started, more than 100,000 pounds of fish were transported by rail in England each year. With a new market of seafood consumers beyond the coasts now reachable, the number of British trawlers increased sixfold in 2 short decades, to more than 800 in the early 1860s.

By the numbers alone, the era when fishermen resisted the advent of the trawl was over. But many still complained that, by ripping up the seafloor and crushing the oyster beds and rocky expanses that were the homes and sources of sustenance for fish, the trawls were killing the goose that laid the golden egg. They clamored so loudly that a royal commission was set up by the British government in 1863 to investigate the complaints. But the commissioners rejected the fishermen's concerns outright, instead claiming--contrary to the facts--that the trawls actually fostered life by furrowing the seabed like a plow turning dirt in a field of wheat.

One of the members of the royal commission was Thomas Henry Huxley. A biologist sporting voluminous sideburns, Huxley had earned prominence as one of the earliest and most vocal supporters of Darwin's views on evolution. But during two royal commission investigations into trawling (the second one undertaken in 1883), Huxley embraced the role of skeptic. He sneered at the fishermen's complaints about dropping catches and dismissed their on-the-water accounts.

By the time the second commission on trawling was launched in 1883, fishing had been revolutionized again by the addition of steam engines. The steam engine allowed trawlers to reach the ocean floor regardless of the conditions, further intensifying the destructive power of the gear. The classic beam trawl was also increasingly joined by the otter trawl, a modification that keeps the front of the net open with steel or wooden doors that gouge out huge furrows and send up an opaque cloud of mud, rocks, seagrass, and anything else that might be in the path of the net. The benefit of the otter trawl for fishers was that it could catch groundfish like cod, not just the flatfish scared up by the beam trawl. In some cases, the otter trawl pumped up fish catches by 50 percent literally overnight.

Fisherman after fisherman testified before Huxley and the commissions, pleading for regulation of the trawls. But Huxley was unmoved. In the same year that the second commission was conducted, he gave the inaugural address to the International Fisheries Exhibition in London. To Huxley, the riches of the British and European seas were still as plentiful as those of the virgin coast of New England had once seemed to John Smith.

I believe that it may be affirmed with confidence that, in relation to our present modes of fishing, a number of the most important sea fisheries, such as the cod fishery, the herring fishery, and the mackerel fishery, are inexhaustible. And I base this conviction on two grounds, first that the multitude of these fishes is so inconceivably great that the number we catch is relatively insignificant; and, secondly, that the magnitude of the destructive agencies at work upon them is so prodigious, that the destruction effected by the fisherman cannot sensibly increase the death-rate.

Five hundred years of complaints against the onslaught of the trawl meant nothing to our doubting Thomas. So convinced was he that the oceans' bounty could not be reduced by the hand of man that he called any regulation of the seas "useless."

A naturalist named Walter Garstang set out to discover over the following decade if Huxley's claim--that "in relation to our present modes of fishing" the sea was inexhaustible--was true; to do so, he launched the first study of the trawl fisheries of England. His findings should have been sobering. Despite the introduction of steam and otter trawls purported to make fishing more efficient than ever, every single trawl fishery on England's east coast saw an overall decline in catches from 1889 to 1898. In Lowestoft, England's easternmost fishing town, overlooking the North Sea, cod catches in 1898 were just 2 percent of what they had been in 1883.

Today, a fishery is often defined as collapsed when catches drop below 10 percent of their historic maximum. Thanks to the brutal efficiency of trawls, England's fisheries were well on their way to oblivion. The willful blindness of Huxley and his contemporaries set an ominous tone for the 20th century. It was in this century that we would fully realize the extent of our collective fishing might.

SPENCER BAIRD HAD BLAMED the messy, voracious bluefish for decimating fish populations in New England, but he had the foresight to warn against the trawler as an even more destructive force. Like the bluefish, trawlers are incredibly wasteful predators, destroying everything in their paths. But unlike the bluefish, which create a buffet for the scavengers traveling in their wake, thereby helping to maintain the existing food web, bottom trawlers leave only rubble, making it difficult for the marine environment to recover to its natural state. Bottom trawlers destroy 4 to 16 pounds of marine life for every fish they catch. This waste, known as bycatch, can include other species of fish (including sharks), sea turtles, dolphins, octopuses, corals, and more--anything that has the misfortune to be caught in the path of a rumbling trawl.

Today's trawlers use much the same technology as in Baird's time. But the difference is twofold. First, in scale: The world's largest supertrawler, the Atlantic Dawn, debuted in 2000. It isn't just a fishing ship. It's a huge floating factory. Weighing 14,000 tons unloaded and stretching longer than 11/2 football fields, the Atlantic Dawn can store 18 million servings of frozen fish in its hold. The ship's otter trawl is supersized, at 200 feet wide and 40 feet tall: A 747 jet could fly through the metal doors. The weighted net is so heavy and powerful that it can sink to the bottom and shove aside 25-ton boulders as it chases down fish.

The second difference is the digital technology. It's been a long time since anyone could catch flatfish by hand in shallow waters, as colonists described with such heady enthusiasm. Modern industrial fishing ships are equipped with satellite technology, seabed-mapping software, sonar, radar, GPS devices, and more tools that transform the ships into highly sophisticated fish-seeking missiles.

Most trawlers aren't nearly as massive as the Atlantic Dawn. Just 1 percent of the world's fishing fleet can be called supertrawlers. But these few massive ships catch a huge portion of the world's seafood.

Meanwhile, in coastal regions and in seas like the Mediterranean, you're more likely to see boats hardly bigger than a large speedboat hauling the otter trawl's telltale steel doors. But what these ships lack in tonnage, they make up for in number. Together with the supertrawlers, they rake a seafloor area twice the size of the continental United States every year. Spencer Baird would be loath to visit New England's remaining fishing ports today. The trawler fleet there fishes an area the size of Rhode Island, Massachusetts, Connecticut, New Hampshire, and Maine combined.

Trawlers are the flagships, so to speak, of a global fleet that has expanded exponentially since the end of World War II. The naturalist Walter Garstang reported that fishing effort had more than tripled on England's shores in the decade he studied the nascent trawling industry, and yet catches were dropping. And now we have added to the weaponry other specialist fishing gear like the purse seine, which targets fish at the top and middle of the ocean's water column. The seiners encircle schooling fish with 1,000-yard nets before dragging them into the hold. Without laws to protect marine mammals, it is purse seiners that are the most likely to drown dolphins and porpoises chasing schooling tuna.

This story has repeated itself again and again on a global scale since the early 20th century. Improved technology has allowed fishing fleets to search farther, deeper, and longer for fish. This expansion is not driven by some unspoken desire to conquer the oceans, like summiting Mount Everest or hiking Death Valley. It's because we've already laid waste to the marine wildlife that was easiest to catch. We started with the slowest and most trusting seabirds and marine mammals (sorry, Steller's sea cows!) and are now in pursuit of the most elusive fish in the world's remotest underwater places.

Take the Patagonian toothfish, for example. Twenty years ago, no one thought to eat this slow-growing deepwater fish, which was found only in the recesses of underwater canyons in the high seas of New Zealand, Antarctica, and southern Chile. But with its tasty and easily cooked meat--and a name change to Chilean sea bass--the once-obscure toothfish suddenly found itself on the menu at upscale restaurants all over the United States in the 1990s. Just as quickly, deepwater longliners started a gold rush on the previously unexploited fish. Only a few years later, toothfish numbers crashed, and it was put on the Monterey Bay Aquarium's red list for overexploited species.

When the modern industrial fleet turns its attention to vogue fish like the Chilean sea bass, the resulting carnage can be breathtaking. Sharks are another devastating example. In the last few decades, the market for shark fin soup has expanded exponentially with the growth of the upwardly mobile Chinese middle class. Once a delicacy reserved for the elite, shark fin soup is now proudly and frequently served at weddings and other important events as a sign of wealth. The shark fin cartilage is tasteless and nutrition free, so any flavor in the clear soup comes from the broth; it is only the shark's symbolic weight that keeps it on Chinese menus.

The fishing industry has responded by waging an all-out war on sharks. Since the fins are so valuable, fishermen haul sharks on board, slice off the fins, and throw the sharks overboard to bleed to death, like poachers kill rhinoceroses just to take their horns. Up to 70 million sharks die this ignominious death every year, carnage equally inhumane and ecologically unsustainable. And because it's extremely difficult to identify a shark species by the fins alone, fishermen get away with slaughtering the most vulnerable sharks, from the fearsome great white shark to the harmless filter-feeding basking shark.

Big predator fish like sharks have suffered huge losses from fishing since the 1950s, when the commercial fleet became fully mechanized after World War II. But just as with the depleted populations of sea turtles brought to light by Jeremy Jackson only in the late 1990s, we've been late to notice sharks' dwindling numbers. As late as 1954, two top academics published a book called The Inexhaustible Sea that echoed Huxley's perennial optimism that the oceans were simply too large for humanity to ever empty of life. And yet the late Ransom Myers and his colleague Boris Worm showed in a landmark study in 2003 that many big predator fish--like tuna, swordfish, marlin, cod, flounder, and halibut--had been reduced to less than 10 percent of their 1950 numbers. And as we've seen, by 1950, many of those fish had already been suffering from intense fishing pressure for some time.

One reason we didn't notice the world's failing fisheries was because it was disguised for years in the official data. If you looked at United Nations figures for global fish catch in the 1990s, it showed a steady increase every year for the entirety of its data set. But Daniel Pauly and Reg Watson, fisheries scientists at the University of British Columbia, were skeptical. China, one of the world's behemoths when it comes to seafood consumption, was consistently reporting jumps in catch every year since the 1980s--a claim that flew in the face of on-the-water reports of diminishing catches. So Pauly and Watson redid the data in 2001, correcting China's overinflated claims and accounting for vast natural fluctuations in the world's biggest fisheries in South America. With the data corrected, the statistics suddenly showed a different story: Global fish catch was not rising. It wasn't even holding steady. Instead, it had peaked in the late 1980s at about 90 million tons and has been in jagged decline ever since, even though we were searching for the most obscure fish in the deepest recesses of the oceans with megaships like the Atlantic Dawn.

There's another reason we haven't noticed the creeping desertification of the once-vibrant seas. We simply fail to remember. Pauly coined the term shifting baseline syndrome in 1995 to describe our collective amnesia when it comes to what constitutes healthy oceans. It's a syndrome with a long pedigree. John Smith, accustomed to the smaller fish common in England's North Sea as a result of centuries of overfishing, showed it with his amazement at the massive codfish abundant in New England's healthy waters.

The concept of shifting baselines was adeptly demonstrated by a doctoral student's project in 2009. Loren McClenachan from the University of California's Scripps Institution of Oceanography pored over hundreds of photos of trophy fish caught in Key West over the last half century. The photographs showed the biggest catches of the day, like groupers, sharks, and sawfish, hung on a wooden dockside rack. In the 1950s photos, huge fish competed for space on the rack, draped one over another. By the 1980s, the fish were small enough to be displayed in nicely contained rows. And by the 2000s, the trophy fish of the day were barely bigger than what you might find in a well-stocked koi pond. Yet today's recreational fishers tacking their best catches to the board and posing for pictures feel just as proud as their predecessors.

It's also hard to talk about shifting baselines when the average American, European, or Japanese person can walk into any grocery store and see huge volumes of seafood from around the world filleted and ready for sale. The supply in just the frozen-foods section of your average Safeway seems inexhaustible! The truth is that most of this fish is imported from far-flung places. It's been a long time since New Englanders could reliably eat huge amounts of cod, herring, and oysters from their own shores. But our appetite for seafood only grows. The supertrawlers, with their onboard fish-processing centers, have made it possible for us to get flash-frozen fish from virtually anywhere in the world, often at the cost of the world's poorest, who stand by as their governments sell the right to fish in their national waters to the highest bidders.